1. Field of the Invention
The present invention relates to a technique for image display.
2. Description of the Related Art
Recently, image display apparatuses with various display units such as a liquid crystal display panel have been put into practical use, including a TV receiver and PC monitor. However, when pursuit for a moving object (way of viewing in which a moving object is pursued by the line of sight on the movie display) is performed on a hold type display apparatus typified by a liquid crystal display apparatus, a motion blur corresponding to the optical output period is observed.
As a technique for reducing such a motion blur, a “spatial frequency division method” has been proposed. The “spatial frequency division method” is a method of doubling the 60-Hz frame rate of an input image signal to 120 Hz, gathering spatial high frequency components of an image regarding a motion blur to one subframe to decrease those of the other subframe, and then displaying the image. In the output image, spatial high frequency components are localized in one subframe, suppressing the motion blur.
In Japanese Patent Laid-Open No. 2009-044460, the frame rate of input image data is doubled. Then, the input image data is divided into spatial high frequency component-emphasized image data and low frequency component image data, and these image data are switched and displayed for respective subframes. At this time, low frequency component image data is formed from the average value of low frequency component image data respectively generated from immediately preceding and succeeding subframes which sandwich the subframe of the low frequency component image data. The use of the average value can reduce a temporal shift of the barycenter on the display of high frequency component-emphasized image data and low frequency component image data. In Japanese Patent Laid-Open No. 2009-044460, a motion blur can be suppressed, and a ghost and tailing blur visually perceived due to a temporal shift of the barycenter can be reduced further.
In Japanese Patent Laid-Open No. 2009-044460, low frequency component image data to be displayed is formed from the average value of low frequency component image data that is respectively generated from immediately preceding and succeeding subframes that sandwich the subframe of the low frequency component image data, as described above. Obtaining the average value of low frequency component image data requires low frequency component image data generated from input image data of at least one immediately preceding subframe. A memory is therefore needed to store low frequency component image data.
When low frequency component image data is lossily compressed to compress the memory band, the compression and decoding generate a compression error, degrading the image quality. In the “spatial frequency division method”, the compression error amount changes depending on the spatial frequency characteristic. For example, even input image data having the same tone value may be visually perceived to have different tone values within the region due to the difference of the frequency characteristic.